1. Field of the Invention
The present invention relates generally to communication systems, and more particularly to call admission control for controlling access to ATM networks or IP networks with support of differentiates services.
2. Description of the Related Art
An Asynchronous Transfer Mode (ATM) network is one method for realizing a flexible and cost-effective network for handling a wide variety of communications. In an ATM network, various types of data that have various transmission rates and traffic characteristics, are multiplexed. Therefore, the multiplexed traffic load fluctuates heavily and rapidly, especially when high speed calls are multiplexed.
Call admission control (CAC) is an important element of ATM traffic management. CAC provides access by regulating the number and types of connections that can be allowed at any given time for a given amount of resources. In an ATM multi-service network, the resource demand of each connection has to be estimated as a function of several variables, including the cell-level traffic descriptions, the required quality-of-service (QOS), the states of the network resources, and the traffic-stream class of priority. When a call request is made, the ATM network determines whether the quality of service would be suitable in all connections, including connections which are already established when the call request is accepted, and determines propriety of the acceptance according to the available services. To make this determination, it is recommended that each terminal issuing a call request should declare parameters, such as an average rate (an average bandwidth) and a peak rate (a peak bandwidth), as source traffic characteristics, and the call admission control be performed using the declared parameters.
ATM admission control can be based on either of two approaches: a direct performance-evaluation approach or an inverse resource-requirement-estimation approach. In the direct approach, the estimated cell-level performance resulting from the admission of a new connection (or call) is calculated. In the inverse approach, an EBR (“equivalent bit rate,” often called the “equivalent bandwidth” or “effective bandwidth”) of the new arrival is determined by some artifice or another. The connection is accepted if the remaining unassigned capacity of the route is not less than the calculated EBR. The EBR for a connection which traverses several links may vary from the link to link and would be based on the source's traffic descriptors, the cell-level performance objectives, the speed of the link under consideration, and the buffer size.
Thus, in the inverse approach, call admission criteria can be expressed as follows:BWup-cbr+BWup-rtvbr+BWup-nrtvbr≦Cp  (1A)BWdown-cbr+BWdown-rtvbr+BWdown-nrtvbr≦Cp  (1B)where BWup-crb, BWup-rtvbr, and BWup-nrvbr are the aggregate effective bandwidth for Constant Bit Rate (CBR), real time Variable Bit Rate (rtVBR) and non-real time Variable Bit Rate (nrtVBR) upstream traffic classes and BWdown-cbr, BWdown-rtvbr, and BWdown-nrtvbr are the aggregate effective bandwidth for CRB, rtVBR and nrtVBR downstream traffic classes, respectively, and Cp is the port bandwidth. When a new connection request, which belongs to a particular class, comes in, it is necessary to recompute the effective bandwidth for that class and then determine if the above criteria in Equations (1A) and (1B) are met.
There are problems, however, with conventional call admission control. For example, in conventional call admission control systems, there is no perfect call admission control or effective bandwidth computation, as the systems generally make approximation of the traffic models. Accordingly, the systems do not have the capacity for maintaining the communication quality or for efficiently utilizing resources of the network when the systems are supplied with calls which have many different traffic characteristics, making precision traffic control difficult to achieve.